Continuous solvent extraction method and apparatus



Sept. 17, 1957 Filed April 1. 1954 R. P. HUTCHINS ET AL CONTINUOUS SOLVENT EXTRACTION METHOD AND APPARATUS FIG CONVEYOR GRUSHER BALL MILL CONVEYOR SCREEN MIXER 3 Sheets-Sheet l MISOELLA EATER INVENTOR RALPH F? HUTCHINS GERALD C. ZWAYER ATTORNEYS P 1957 R. P. HUTCHINS ETAL 2,806,770

CONTINUOUS SOLVENT EXTRACTION METHOD AND APPARATUS Filed April 1. 1954 3 Sheets-Sheet 2 FIG.2

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ATTORNEY:

p 1957 R. P. HUTCHINS ET AL 2,806,770

commuous SOLVENT EXTRACTION METHOD AND APPARATUS Filed April 1. 1954 3 Sheets-Sheet 3 FIG; 3'

I T o o. 32 sjr AM o; crla 33 NR 8| COOLER i i r A CARBDN I E 79 Nelson. [.80 LIQUID W HEXHAUST :27:: L'ZT OUTSIDE INVENTOR RALPH P. HUTCHINS GERALD C. ZWAYER ATTORNEY-6 2,806,179 Patented Sept. 17, we?

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CONTINUUUS'ISGLVENT EXTRAQITIQN P/EETHGD AND APPARATUS Ralph P; Hutchins'and Gerald 'C.'Zwayer, Pique, @hio,

- assignors to The French Gil 'lviill Machinery Company, Piqua, Ohio Application'April 1,1954, Serial No. 420,424

4 Claims. (Cl. 2331t This invention relates 'to the extraction of sulfur from "its ore, and more particularly by solvent extraction.

"Anobject of the invention is to provide an improved apparatus and method for the solvent extraction of sulfur from its ore, with the use of which sulfur may be obtaincd frorn its ores in exceptionally pure form and at a cost which makes this process and equipment economically practical, and which requires relatively simple equipment,-and which maybe carried 'on continuously.

Various other objects and advantages will be apparent from the following description of one embodiment illustrating the invention.

In the accompanying drawings:

Figs. 1, 2 and 3 represent respectively three adjoining parts of'a complete equipment for the practice of this invention, it being understood that Figs. 1, 2 and 3 are 'to be disposed side by side in that order so as to illustrate togetherone solvent extraction system operable in accordance with this invention.

In the'illustrated embodiment of the invention, the

sulfur ore is brought to the equipment in a suitable ore conveyor-L from which it is discharged into a suitable crusher 2, in which the ore is reduced to loose particles of moderatesize. The ore from the crusher is delivered by a conduit 3 to a suitable ball mill 4, in whichthe ore isreduced to relatively small particles, largely a'pow'der. The finely divided ore is delivered by the ball mill through a conduit5' to a suitable-vibratory or oscillatory screen 6 which is'mechanically operated so as to pass the ore particles'that are below a specified maximum size through a Iconduit'7 into a surge bin 8. The larger particles of ore which do not pass through the screen are delivered into a suitable conveyor 9 which elevates them and discharges them back into the baH mill, and in passing through the ball mill the second time, they are reduced to a finely divided condition.

The surge bin maintains the finely divided ore above a minimum level at all times to prevent the escape of solvent through the ingoing ore. From the bottom of the surge bin a variable speed feeder 10 conveys the finely divided ore progressively into a mixer 12.. The conveyor it) may be a slowly rotating screw conveyor or any other conveyor which feeds the ore particles at a desired rate, and is always filled so as to present a barrier to'the'escape of free solvent from the mixer. A solventcontaining miscella is supplied through a pipe 12 to the mixer where the ore particles are formed into a slurry. The solvent used for the sulfur is carbon disulphide. This slurry of ore and miscella which carries the solvent is withdrawn from the bottom of the mixer through a pipe 13 leading to the intake side or" a pump 14. This pump is preferably a variable speed driven, positive, displacement pum' or it may be a metering valve if an ordinary pump is used or if the mixer is placed above the extractor so as to feed by gravity to the extractor.

The discharge side of the pump 14 is connected by a pipe 15 to the top of an extractor 16. This extractor is a long, closed tubing of substantial diameter in upright between the top of the extractor chamber andgthe discharge end 17 of the pipe 15 that serves "as a settling area where fines or small particles of the ore can settle out of the miscella. The lower end of the extractor is c9n nected bya pipe 18 to the intake side of a of the variable speed dfiv'en, positive displacement typ The discharge side of the ample is connected a pipe 20 to the upper part of a de's'olventizer 21. T his 'des'olve'ntizer is of a type well known the art forthe removal of solvent from small solids. It comprises a plurality of superposed chambers through which the solidsprogres' sively pass in succession, and in which they are ri'echanically'stirred during their 'siowpassageby gravity from chamber to chamber. v

A pipe zz'suppi i'ng live ste'a'ni tinder prssui'e is connectedto each chamber of the desolventizer eas to discharge spar'ging steam into the mass of solids iiieach chamber, that not only heats theparticles being stirred or agitated, but strips the solvent from those particles. The chambers in the desolventiier may be steam jacketed if desiredfin order to heat the ore particle's't o a temperature at which the solvent will be driveno 'f,'bi1t1usually We have foundthat the spar'ging steam admitted pipe 22 is usually suificient to heat the ore and remove the solvent without the use of heated wallsreruie'chagnbers. The spent 'ore from which the solventhas been removed-is then dischafg'ed'thro'ughacohduitjf lii'asmuch as these desolv'enti'zers with mechanical s" er'sior mixers in the various chambers are known in mean, they have been illustrated only schematically. p

The vapors from the top of the desolven'tiz erz l which contain some water vapora'nd solvent are conveyed by a conduit 24 intofa suitable vapor washer 25 in which the vapors are washed to remove entrained solid particles without condensing the solvent, [and their the solvent vaporsare passed through aboriduit 2 6irito a condenser 27. The condensed fvapors from thehon dehser '27 are conveyed by a pipe 28 into the top of a .solvent work and water separating tank 29 Any"ur c'ondensedvapors from the condenser 27 are conveyed insuccession through pipes 3B, 31 and32 to an'air cooler 33 inwhichfurther condensation of vapors can take place. The condensed vapors from the air cooler 33are conveyed through pipe 34 to the top of the solvent work and water separating tank 29through the inlet pipe 23.

The solvent work and Water separation tank obtainable in the open market under that name and, therefore, it is shownonly schematically. It is a combination tank with a bame down the middle. One side is used as a water separating tank in which the solvent and water coming from the condenser are allowedto' separateiby their differences in density. The carbon disulphide being heavier than water will settle to the bottom'and the water will rest upon'it. The solvent passes'over into th'e work tan'l; side through piping comingolr the botto m'a nd rising to a desired point to maintain theint'erfa'ce level at about two-thirds the height of the tank. The water flows olf continuously through a pipe leading from; the topof the tank. The bafile is as'olid one, so that there is no connection between the two parts of the tankexc'ept through the pipe line coming fromth'e bottom of the sepmatihn side and rising inside the tan to a point; near the t op, where it discharges into the work tankQside. I p p A level indicator 35 with pipe co'nhection lw' itofthe tank above the interface 'lev'el'and the pipeco ecticnf37 to the tank below the interface level indicates the rface level'inthe'separator tank. A similar level fdicator 38 is similarly indicated by pip'es 39 and '40 to the worktahk. of solvent so as to indicate the level of the solvent in actual bottom of the still.

a 3 the work tank at all times. Solvent is withdrawn from the work tank side of tank 29 by a pipe 41 which is connected to the intake side of a continuously operating 42, and the discharge side of the pump is connected by'a'pipe 43 to a miscella heater 44, Fig. 1. From the unisce lla hea'ter the miscella or solvent passes through pipe =12'to the mixer. This heater 44 may be of any suitable *construction that will heat the miscella and solvent as they .ipass to the mixer. The waste water from the tank 29 is -*-conducted through a pipe 45 to sewer.

From the pipe 43 a branch 46, Fig. 2, leads to the lower part of the extractor 16 and there opens into the extractor a substantial distance above its bottom. This leaves in the bottom of the extractor tube a settling chamber through which the ore may settle out after it has passed through the stream of solvent which enters from the pipe 46 into the extractor and passes upwardly through the extractor to substantially its top. A pipe 47 opens from the top of the extractor well above the inlet 17 from the pipe 15, and discharges into a miscella surge tank 48. The miscella in this surge tank 48 is removed by a pump 49 which is connected at its intake side to the bottom of the surge tank, and at its output side by a pipe 50 which {passes to a filter 51 in which any fine solids in the miscella -'are removed therefrom.

After filtering in filter 51, the miscella is conveyed by a pipe 52 to the lower end of a pre-evaporator 53, Fig. 3. This pre-evaporator 53 is of the long tube type, usually f steam-jacketed, which is well known in the evaporation industry, and is also called a rising film type of unit. The reason it is a film type is because the volatile solvent is evaporated as soon as the miscella enters the heated tube area, and the vapor expands so rapidly that the mixture of vapor and liquid is forced at a high velocity upwardly through the heated tube. high heat transfer coetficient and makes this type of t This very high velocity gives a evaporator very efiicient.

The top of the evaporator 53 is connected by a conduit :54 to a centrifugal type of entrainment separator 55.

The mixture of vapor and liquid from the top of the evaporator 53 is thrown at high velocity into. this separator 55 and the liquid collects on the outer wall of the chamber of this separator and runs down into the bottom which opens into a pipe 56. The vapors swirl around in a pattern identical to the movement of air in a cyclone separator, and then pass out in an upward direction A vapor vent pipe 69 leads from the top of the filter 51 to a common vent line 70 that is connected to the pipe 32 that leads to the air cooler 33. A vapor vent pipe 71 leads from the extreme top of the extractor 16 to this common vent line 70, and a vapor vent pipe 72 leads from the top of the miscella surge tank 48 to vent line 70. The vent line 70 extends to the top penis mixer 11 so that any vapors released in the mixer may pass through the vent line 70 and the pipe 32 to "the "air cooler 33.

The pipe 50, which leads from the pump 49 that draws the miscella from the bottom of the surge tank 48, is provided with a branch pipe 75 which leads to the pipe 43 that conveys miscella to the miscella heater 44, Fig. 1. This branch pipe 75 is provided with a valve 76 therein by which the flow of miscella from the surge tank 48 to the heater 44 may be controlled, and the pipe 50, between the connection to the pipe 75 and the filter 51, is also provided with a control valve 77 which further aids in controlling the proportions of the miscella which are sent through the filter and to the mixer 11 through the heater 44.

Referring now to the air cooler 33, Fig. 3, any uncondensed vapors therein are conveyed through a pipe 78 through a carbon adsorber 79. As'these vapors pass through this carbon adsorber, any solvent escaping beyond the air cooler is adsorbed by the activated carbon. The air or other gas which passes the carbon adsorber is then discharged to exhaust through pipe 80. There are two of these carbon adsorbers 79 which are operated alternately, and the unit not in service is re-activated by sending live steam through it, which drives ofi the solvent that was adsorbed by the carbon, and this driven-off solvent is conducted by pipe 81 to a steam-out condenser 82 which again condenses the solvent from pipe 81 and returns it to the air cooler 33, Where it passes with the other condensed vapors through pipe 34 to tank 29.

In the operation of this illustrated apparatus, the ore is reduced by the crusher 2 and ball mill 4 or other suitable pulverizer to a finely divided condition and the fine particles are delivered into the surge bin 8. The large particles that do not pass through the screen are returned to the ball mill and there further reduced to the desired 1 particle size that will pass the screen.

From the surge bin the fine partlcles of ore are passed in a continuous stream mm the mixer 11, to which miscella containing the solvent,

carbon disulphide is also admitted to form a slurry. It

Any vapors still uncondensed in the condenser 58 are conducted through pipes 60, 61 and 32 to the air cooler 33.

The liquid from the centrifugal type of separator 55 passes through pipe 56 to the top of a final still 62, which is also called a stripping column. This column is preferably of the disc and donut construction, well known in the art, and is steam-jacketed so as to keep the temperature within the still in the maximum range between 245 degrees F. to 320 degrees F. The preferable range of temperature is between 260 degrees F. and 300 degrees F. and usually is in the narrow range between 290 degrees F. and 300 degrees F., but is never above about 320 degrees F. Sparging steam is admitted to the lower part of this still 62'through a pipe 63 at some distance above the Liquid. sulfur is withdrawn from the bottom of the still, below the point at which the sparging steam is admitted to a pipe 64. The top of the still 62 is connected by a conduit 65 to a condenser 66 in which solvent vapors are condensed. The condensed vapors from the condenser 66 are conducted through a pipe 67 to the pipe 28 that leads to the top of thesolvent work and water separating tank 29. Any uncondensed vapors in the condenser 66 are conveyed by a pipe 68 to the pipe 61, and then by pipe 32 to the air cooler 33.

has been found that if the dry ore is introduced directly into the extraction chamber, it tends to plug the extractor and the operation is unsatisfactory. It is therefore important to have the dry ore wetted, such as with the miscella, into a slurry form before it is admitted to the extractor. In the extractor the ore particles settle slowly therethrough, and at the same time miscella containing the solvent passes upwardly through the extraction chamher in counter flow to themovement of the ore downwardly.

In other words, the miscella containing the solvent moves slowly upwardly as a stream through the extractor chamber and out into the miscella surge tank 48; At the same time, the ore slurry is delivered to the top of that chamber so that the ore wetted with the solvent settles downwardly through the upwardly moving stream of solvent and miscella. During this counterflow movement of ore and solvent, the sulfur is extracted from the ore by the solvent and carried with the solvent into the surge tank 43. The ore from which the sulfur has been extracted settles to the bottom of the extraction chamber where it is removed by thepurnp and delivered to the desolventizer 21. Because the miscella and solvent enter the extraction chamber well above the bottom of that chamber, the ore including the fines can settle out into the bottom of the extraction chamber and remain there 7 until removed therefrom by the pump 19. 7 5

Similarly, the delivery of the slurry of ore into the extraction chamber below the point where the liquid is removed, enables any fines which are carried upwardly by the stream of liquid to settle out and not be carried over into the surge tank except to a very minor extent. Because of the settling spaces at the top and bottom of the extractor chamber, most of the solids can settle out and provide a rather clear miscella of carbon disulphide and sulfur. Because the fresh solvent engages the ore particles after most of the extraction has occurred, maximum extraction of the sulfur from the ore is possible. The solvent-saturated solids which are substantially free of sulfur are pumped or metered into the desolventizer where the solvent is removed from the spent ore.

Part of the miscella removed from the extractor and collected in the surge tank 48 is returned to the mixer for making a fresh slurry with the fresh ore, and the balance is passed through the filter and then conducted through the pre-evaporator, then through the separator 55. The liquid from the separator 55, which contains solvent and sulfur, is then passed through the final still 62, where the solvent is driven off and the sulfur in liquid form is removed from the bottom of the still. In the evaporator 53, a temperature of about 290 degrees F. is maintained, which causes some of the solvent to be evaporated, which leaves a concentrated miscella containing about 97% sulfur. This concentrated miscella at a temperature of about 290 degrees F. then passes downwardly through the final still or stripping column which has steam-jacketed sections along it, so that the temperature of the liquid sulfur can be maintained preferably at about 290 degrees F.

We have found that a very small amount of solvent in the miscella will keep the sulfur in solution at temperatures far below 260 degrees F., so that in the pre-evaporator 53 as long as some solvent is allowed to remain, it is possible to operate at a temperature below 290 degrees F. It is necessary to be certain that if the solvent is removed, there will be sufficient heat available to supply the 16 B. t. u.s per pound that sulphur requires as its heat of fusion to remain liquid. To avoid danger of the sulfur setting up or becoming a solid, it is preferable to maintain a temperature in the pre-evaporator and the final still of around 290 degrees F. to 300 degrees F.

The heat in the pre-evaporator and the final still, except for the sparge steam admitted to the final still, is supplied by a steam chest with vertical tubes rolled into tube plates. The miscella preferably flows inside the tubes and the steam is in the chest outside the tubes. It is important, particularly in the final still 62, that the temperature of the contents never be increased beyond about 320 degrees F. because once the sulfur is turned into a thick, viscous mass, it will not convert readily back to the less viscous liquid, even though the temperature has dropped.

The solvent from the desolventizer is condensed along with moisture vapors and delivered to the solvent work and water separator tank where the water and liquid solvent are separated and the solvent returned to the recovery system for use in treating further ores. Sulfur pumped out of the ground in a solution or melted state is about 99.5% pure, but the sulfur obtained from the solvent extraction process is about 99.9% pure, so that a much purer sulfur is possible by this invention.

It will be understood that various changes in the details, materials, steps and arrangement of .parts which have been herein described and illustrated in order to explain the nature of the invention may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

We claim:

1. Apparatus for the solvent extraction of sulfur from its ore, which comprises means for forming a slurry of solvent and finely divided particles of said ore, a solvent extraction element connected to said means and receiving slurry therefrom, means for circulating a solvent containing liquid through said element in prolonged contact with said slurry, means connected to said element for receiving and filtering the solvent containing liquid after it passes through said element, desolventizer means connected to said element for receiving therefrom the extracted ore particles and removing and recovering solvent that is ad herent to said particles, a pro-evaporator heater connected to said filter means to receive therefrom the filtered liquid and heat it to a temperature above the vaporization point of said solvent to form solvent vapor, a separator of the centrifugal type connected to said heater to receive therefrom the heated liquid and vapors from said heater and separate the vapors and liquid therein, a condenser connected to said separator for receiving and condensing said separated vapors, a stripping still connected at its upper end to said separator to receive the separated liquid, and having an outlet for liquid at its bottom, means for heating the liquid in said still to keep the liquid against solidifying, and means for passing sparging steam upwardly through the liquid in said still to remove remaining solvent therefrom.

2. The apparatus as set forth in claim 1, and a solvent and water separator connected to all of said condensers for receiving condensed vapors and separating the solvent and water therein by stratification, and a connection from said last mentioned separator to said slurry forming means for delivering separated solvent back to the slurry forming means.

3. The apparatus as set forth in claim 1, the pre-evaporator being of the rising film type.

4. The method of recovering sulfur from a miscella of sulfur, its ore solids and a solvent coming from a sulfur extraction operation, which comprises filtering said miscella and solvent, to remove ore solids therefrom, passing the filtered miscella and solvent in a rising, confined steam, heating the rising stream to a temperature of about 290 degrees F. at a rate which vaporizes a part only of the solvent of said stream that by vapor expansion causes the heated stream and vapor to move along at a high velocity, centrifugally separating the liquid and the vaporized part only of this high velocity stream, condensing and collecting the separated vapors, passing the separated liquid containing the remaining solvent downwardly through a stripping column at a temperature between 245 degrees F. and 320 degrees F., passing sparging steam upwardly through the downwardly moving liquid in said column, removing liquid sulfur from the bottom of said column, and removing and condensing solvent vapors from the upper part of said column.

References Cited in the file of this patent UNITED STATES PATENTS 1,963,921 Nagelvoort June 19, 1934 2,088,190 Du Pont July 27, 1937 2,419,310 Belchetz Apr. 22, 1947 2,508,002 Swenson May 16, 1950 2,537,842 McGualey et al. Ian. 9, 1951 

4. THE METHOD OF RECOVERING SULFUR FROM A MISCALLA OF SULFUR, ITS ORE SOLIDS AND A SOLVENT COMMING FROM A SULFUR EXTRACTION OPERATION, WHICH COMPRISES FLITERING SAID MISCALLA AND SOLVENT, TO REMOVE ORE SOLIDS THEREFROM PASSING THE FILTERED MISCALLA AND SOLVENT IN A RISING, CONFINED STEAM HEATING THE RISIN STEAM TO A TEMPERATURE OF ABOUT 290 DEGREE F. AT A RATE WHICH VAPORIZED A PART ONLY OF THE SOLVENT OF SAID STEAM THAT BY VAPOR EXPANSION CAUSES THE HEATED STREAM AND VAPOR TO MOVE ALONG AT A HIGH VELOCITY, CENTRIFUGALLY SEPARATING THE LIQUUID AND THE VAPORIZED PART ONLY OF THIS HIGH VELOCITY STREAM, CONDENSING AND COLLECTING THE SEPERATED VAPORS, PASSING THE SEPERATED LIQUID CONTTAINING THE RAMINING SOLVENT DOWNWARDLY THROUGH A STRIPPING COLUMN AT A TEMPERATURE BETWEEN 245 DEGREES F. AND 320 DEGREES F., PASSING SPARGING STEAM UPWARDLY THROUGH THE DOWNWARDLY MOVING LIQUID IN SAID COLUMN, REMOVING LIQUID SULFUR FROM TH BOTTOM OF SAID COLUMN, AND REMOVING AND CONDINSING SOLBENT VAPORS FROM THE UPPER PART OF SAID COLUMN. 